Liberation

At the beginning of all campaign maps, there is a dialog box that asks whether to disable the AI heroes from fleeing the battlefield (yes/no). In my case, no one fled.

I know about this window, and I intentionally didn't activate it. In that situation, I didn't really care whether the enemy hero fled or not, because the war was already won anyway. However, the fact that the two demons, with whom I had to fight key battles, fled beforehand, was actually very beneficial to me, as it allowed me to save a couple of archers, of which I had barely managed to gather enough in two weeks.